Due to the absence of electrodes, electrodeless fluorescent lamps have longer lifetimes than fluorescent lamps with electrodes, and have efficiencies as high as those of common fluorescent lamps. With such characteristics, electrodeless fluorescent lamps have been drawing public attention from the point of view of environmental protection and economic efficiency, and have a potential for becoming more and more widespread in the future. Electrodeless fluorescent lamps are demanded primarily as an alternative light source replacing incandescent lamps, which have been widely used in general lighting. Where electrodeless fluorescent lamps are used for this purpose, they are required to be as compact as incandescent lamps, have high lamp efficiencies and be economical.
Electrodeless fluorescent lamps, having higher efficiencies and longer lifetimes than fluorescent lamps with electrodes, can be suitable light sources. For example, commercially-available electrodeless fluorescent lamps use operating frequencies in a MHz frequency range such as 13.56 MHz, being an ISM band, the rated power of these lamps is about 25 W to 150 W, and the lifetime thereof is 15,000 to 60,000 hours. It has been shown that they have desirable maintainability and efficiency.
These electrodeless fluorescent lamps that are being sold in the market today are primarily used for lighting at locations where replacing lamps requires a high cost, such as landscape lighting, street lighting, bridge lighting, public park lighting, lighting for factories with high ceilings, etc., and most of them use separate ballast circuits.
In recent years, self-ballasted electrodeless fluorescent lamps have been developed in the art that can be plugged into incandescent-lamp sockets and used as if they were incandescent lamps, while retaining the advantageous characteristics of electrodeless fluorescent lamps such as the high efficiencies and long lifetimes. Discussions have been made on widely spreading self-ballasted electrodeless fluorescent lamp having such advantageous characteristics as an alternative light source replacing incandescent lamps. Specifically, self-ballasted electrodeless fluorescent lamps including a discharge bulb and a ballast circuit integrated as one unit have been developed in the art and expected to become widespread, which can be plugged into incandescent-lamp sockets so that they can be used as an alternative light source replacing incandescent lamps at locations where incandescent lamps have conventionally been used, such as hotels, restaurants and houses.
The electrodeless fluorescent lamps required as an incandescent lamp replacement, unlike those used for public outdoor lighting, are those that have a luminous flux equivalent to that of an incandescent lamp of 60 W to 100 W and have a wattage of about 10 W to 20 W. There is a demand for these low-wattage electrodeless fluorescent lamps as an incandescent lamp replacement to not only have long lifetimes but also be compact, readily acceptable pricewise, and free of electromagnetic interference (EMI) with surrounding electric appliances.
A primary object of the present invention, which has been made in view of the above, is to provide an electrodeless discharge lamp operating device that exhibits desirable characteristics (particularly, maintaining a stable discharge) even in an electrodeless discharge lamp operating device in which electromagnetic interference (EMI) is suppressed.